The present invention provides organosilicon compounds containing an aromatic moiety group and methods for using the same for the solid-phase synthesis of libraries of compounds.
Combinatorial chemistry, combined with recent advances in robotic screening which enable the testing of a large number of compounds in a short period of time, is becoming an important tool in accelerating drug discovery. This technique generally involves the preparation of a large number of structurally related compounds either as mixtures in the same reaction vessel or individually by parallel synthesis. In this manner large pools of similar compounds can be synthesized rather quickly. Combinatorial libraries have been prepared using both solution chemistry and by solid phase synthesis. Solid phase synthesis allows the use of excess reagents to drive the reaction to near completion, and easy removal of the reagents and side-products by simple washing with solvent. Therefore, solid phase synthesis generally offers a more attractive approach to the generation of combinatorial libraries.
One of the key elements in solid phase chemistry is the polymeric resin. Many of the resins which are currently employed were originally developed for the synthesis of peptides. Polar functionality such as carboxylic acids and amides were released upon cleavage of products from the resins. Recent advances in linker technology allowed other polar functional groups such as an alcohol and a thiol to be attached to the polymer support. However, most of the linkers available for solid support synthesis to date require polar functional groups for binding and release the same polar groups after cleavage. For the generation of libraries of biological activity, such polar functionalities may possess unfavorable pharmacological properties. In many cases, attempts have been made to render the lead compounds found in vitro less polar to increase the pharmacological properties such as high cellular uptake and hydrophobic membrane transport. Therefore, the focus in this field has been on designing new solid support linkers for non-polar or aromatic compounds which are commonly found in pharmaceutical agents.
To address this concern, several novel strategies utilizing resin. bound arylsilane as a xe2x80x9ctraceless linkerxe2x80x9d have been developed for solid phase synthesis of aromatics or heteroaromatic compounds. This method allows the attachment of substrates to the support at an inert site within the molecule. Upon cleavage from the resin by desilylation (with TFA, HF, or TBAF), no trace or xe2x80x9cmemoryxe2x80x9d of attachment to the polymer support is left. Also, silicone-directed ipso-substitution of arylsilanes is frequently used for regiospecific introduction of electrophilic functional groups such as bromine and iodine to the aromatic ring. (see for example, Chan et al., xe2x80x9cElectrophilic substitution of organosilicon compounds. Applications to organic synthesis,xe2x80x9d Synthesis 1979, 761-786; Han et al., xe2x80x9cSilicon directed ipso-substitution of polymer bound arylsilanes: Preparation of biaryls via the Suzuki cross reaction,xe2x80x9d Tet. Lett. 1996, 37, 2703-2706) Therefore, silicon-based linkers have been proved to be useful tools for the traceless synthesis of aromatics or halide substituted aromatics.
To date, several different arylsilane linkers have been devised and employed for the solid-phase synthesis of diverse aromatic systems. (see for example, Plunkett et al., xe2x80x9cGermanium and silicon linking strategies for traceless solid-phase synthesis,xe2x80x9d J. Org. Chem. 1997, 62, 1885-2893; Chenera et al., xe2x80x9cProtodetachable arylsilane polymer linkages for use in solid phase organic synthesis,xe2x80x9d J. Am. Chem. Soc. 1995, 117, 11999-12000; Boehm et al., xe2x80x9cDevelopment of a novel silyl ether linker for solid-phase organic synthesis,xe2x80x9d J. Org. Chem. 1996, 61, 6498-6499; Woolard et al., xe2x80x9cA silicon linker for direct loading of aromatic compounds to supports. Traceless synthesis of pyridine-based tricyclics,xe2x80x9d J. Org. Chem. 1997, 62, 6102-6103, Hu et al., xe2x80x9cNovel polymer-supported trialkylsilanes and their use in solid-phase organic synthesis,xe2x80x9d J. Org. Chem. 1998, 63, 4518-4521; and PCT Publication Nos. WO 98/05671 and WO 98/17695) Most of the known silicone linkers are generally designed to facilitate the solid-phase synthesis of focused libraries of aromatics, such as 1,4-benzodiazephines, biaryls, benzofurans, and tricyclics. Some of the silicone based linkers, [for example, (4-bromophenyl)diisopropylsilyloxymethyl polystyrene, (4-formylphenyl)diisopropylsilyloxymethyl polystyrene, and (4-trityloxyphenyl)diisopropylsilyloxymethyl polystyrene] from commercial sources are designed for the solid phase organic synthesis of substituted benzenes.
One of the limitations associated with the linkers described above is that linker itself has to be attached to the polymer by reaction of the polar group (alcohol, or carboxylic acid). Polar groups on the aromatic ring which would be utilized for attachment to the polymer requires protection/deprotection steps during the construction of other desired functional group on the aromatic. This protection/deprotection step requirement slows the construction of silyl linker. In addition, in some cases many functional groups can not be introduced due to compatibility problems. The other limitation of these linkers is that the appropriately functionalized aryl group must be first attached to the silicon linker, prior to attaching it to the solid support. Therefore, a separate linker must be prepared for each aryl group. To overcome this limitation, (4-methoxyphenyl)dimethylsilylpropyl polystyrene has been developed. Although this linker can be used to attach various aryllithiums or Grignard reagents to form the appropriate arylsilyl linkage, the application is still limited because other essential functional groups on the aryl ring must be able to tolerate strong basic conditions and/or must be protected.
Completely different class of linkers for traceless synthesis of arenes is triazine-based resins. Reaction of diazonium compound to the N-benzylaminomethyl polystyrene (or piperazinomethyl polystyrene) leads to formation of a polymer bound triazine. This functionality is stable under a wide range of reaction conditions (e.g., n-BuLi and DIBAL) but is readily cleaved by treatment with HCl in THF to liberate the aromatic moieties containing hydrogen at the original point of attachment. Although this approach is generally applicable to a wide range of simple anilines, other functional groups (which would be used for diversification) attached to the aniline are limited to ones which can tolerate acidic conditions employed for diazotization.
Despite these advances in a solid-support chemistry, there is a need for compounds which are useful in the solid-phase synthesis of aromatic containing molecules.
One embodiment of the present invention provides a compound of the formula: 
wherein
each of R1 and R2 is independently aryl, C1-C6 alkyl, or C3-C20 cycloalkyl;
R3 is a bond or C1-C10 alkylene;
R4 is C1-C10 alkylene;
each of R5, R6 and R7 is independently H or C1-C6 alkyl;
Ar1 is aryl or heteroaryl; and
X is a functional group.
Another embodiment of the present invention provides a resin-bound compound of the formula: 
where Ar1, R1, R2, R3, R4, R5, R6, R7, and X are those described above, L1 is a bond or a link and P is a solid-support.
Another embodiment of the present invention provides a method for preparing a resin-bound compound comprising coupling a silane compound, preferably of formula I described above, to a polymeric resin using a transition metal, preferably palladium, mediated coupling reaction. Preferably, the silane compound comprises an alkenyl moiety, which allows a formation of silylalkylborane compound when the alkenyl moiety is contacted with a hydroborating agent. The silylalkylborane compound can be coupled to a polymeric resin which has an aryl halide moiety. In this manner, the coupling reaction results in a formation of a covalent bond between the carbon bonded to the boron atom and the carbon atom of the aryl halide moiety of the polymeric resin which is bonded to the halide.
The method of the present invention can also include linking the polymeric resin with a linker which has the above described aryl halide moiety. Preferably, the linker is of the formula X1xe2x80x94Phxe2x80x94C(xe2x95x90O)OR13, where X1 is a halide and R13 is H or C1-C6 alkyl. It should be appreciated, however, that when the linker is linked to a resin containing an amine group, e.g., a moiety of the formula H2N-(Resin), the resulting linker coupled resin will have an amide bond, e.g., the resulting linker coupled resin is of the formula: X1xe2x80x94Phxe2x80x94C(xe2x95x90O)xe2x80x94NHxe2x80x94(Resin).
Alternatively, the silylalkylborane compound can be oxidized to form a silylalkylhydroxy compound prior to the coupling step. Moreover, the hydroxy group of the silylalkylhydroxy compound can be converted to an amine, carboxylate or other functional groups to allow coupling with polymeric resins such as Merrifield resin, Wang resin, aminomethylated polystyrene resin, Rink resin, and aminomethylated Tentage) resin.
Still yet another embodiment of the present invention provides a method for preparing a library of compounds comprising an aromatic group, wherein the aromatic group comprises an aryl group or a heteroaryl group. Methods for generating a library of compounds include:
(a) preparing a plurality of resin-bound compounds described above;
(b) optionally dividing the resin-bound compounds into a plurality of portions;
(c) performing additional synthetic chemistry to modify the functional group X to produce modified resin-bound compounds;
(d) optionally recombining the portions; and
(e) cleaving at least a portion of the modified resin-bound compounds from the polymeric resin supports so that the aromatic groups resulting from the cleavage have a hydrogen, halide, hydroxy or acyloxy group on the aromatic carbon which were bound to the polymeric resin through the silyl group.
The steps of (b) dividing resin-bound compounds, (c) performing additional synthetic chemistry, and (d) combining the portions can be repeated to generate larger compounds.
The compounds can be cleaved from the polymeric resin support by treatment with a cleaving agent including an acid, a fluoride ion source, an electrophile, and mixtures thereof.
By using a suitable assay, compounds or libraries of compounds of the present invention can be tested to identify or determine a ligand for a particular receptor.
The standard method for conducting a search for new chemical moieties that can effectively modulate a variety of biological processes is to screen a variety of pre-existing chemical moieties, for example, naturally occurring compounds or compounds which exist in synthetic libraries or databanks. The biological activity of the pre-exiting chemical moieties is typically determined by applying the moieties to an assay which has been designed to test a particular property of the chemical moiety being screened, for example, a receptor binding assay which tests the ability of the moiety to bind to a particular receptor site.
In an effort to reduce the time and expense involved in screening a large number of randomly chosen compounds for biological activity, several developments have been made to provide libraries of compounds for the discovery of lead compounds. The chemical generation of molecular diversity has become a major tool in the search for novel lead structures. Currently, the known methods for chemically generating large numbers of molecularly diverse compounds generally involve the use of solid phase synthesis, in particular to synthesize and identify peptides and peptide libraries.
The present invention provides compounds which are useful for solid-phase synthesis of not only peptides but also for non-peptide compounds, methods for linking these compounds to functionalized solid supports (e.g., halogenated polystyrene resin), methods for using the solid-support bound compounds to generate libraries of compounds, and methods for using them in screening processes. In particular, compounds of the present invention include a functionalized aryl moiety. Specifically, compounds of the present invention have the following general formula: 
where each of R1 and R2 is independently aryl, C1-C6 alkyl, or C3-C20 cycloalkyl, preferably, R1 and R2 are methyl; R3 is a bond or C1-C10 alkylene, preferably R3 is a bond or C1-C6 alkylene; R4 is C1-C10 alkylene, preferably R4 is methylene (i.e., xe2x80x94CH2xe2x80x94); each of R5, R6 and R7 is independently H or C1-C6 alkyl, preferably R5, R6 and R7 are H; Ar1 is aryl or heteroaryl, preferably Ar1 is optionally substituted phenyl, naphthyl, thiophenyl, pyridyl, biphenyl, quinolinyl, thiazinyl, isoquinolinyl, imidazolyl, furanyl, fluorenyl, indolyl, or indanyl; and X is a functional group, preferably X is a halide, substituted aryl or heteroaryl, or a moiety of the formula xe2x80x94NR8R9, xe2x80x94NHNR10, xe2x80x94OR11, xe2x80x94SR12, xe2x80x94CN, xe2x80x94CHO, xe2x80x94CO2R13, xe2x80x94CR14CR15CO2R13, xe2x80x94C(xe2x95x90O)NR16R17, xe2x80x94CR14xe2x95x90CR15C(xe2x95x90O)NR16R17, xe2x80x94CH[CH2(NR8R9)]CO2R13, or xe2x80x94CH(NR8R9)CO2R13, where each of R8 and R9 is independently H, C1-C6 alkyl, or an amine protecting group, R10 is H, C1-C6 alkyl, or a hydrazine protecting group; R11 is H, C1-C6 alkyl, or a hydroxy protecting group; R12 is H, C1-C6 alkyl, or a thiol protecting group; each of R13, R14, and R15 is independently H, or C1-C6 alkyl; and each of R16 and R17 is independently H, C1-C6 alkyl, or an amide protecting group. More preferably, X is substituted aryl or heteroaryl, xe2x80x94NHR9, xe2x80x94NHNR10, xe2x80x94OR11, xe2x80x94SR12, xe2x80x94CN, xe2x80x94CHO, xe2x80x94CO2R13, xe2x80x94CHxe2x95x90CHCO2R13, xe2x80x94CH[CH2(NR8R9)]CO2R13, or xe2x80x94CH(NR8R9)CO2R13.
The term xe2x80x9calkylxe2x80x9d refers to aliphatic hydrocarbons which can be straight or branched chain groups. Alkyl groups optionally can be substituted with one or more substituents, such as a halogen, alkenyl, alkynyl, aryl, hydroxy, amino, thio, alkoxy, carboxy, oxo or cycloalkyl. There may be optionally inserted along the alkyl group one or more oxygen, sulfur or substituted or unsubstituted nitrogen atoms. Exemplary alkyl groups include methyl, ethyl, i-propyl, n-butyl, t-butyl, fluoromethyl, difluoromethyl, trifluoromethyl, chloromethyl, trichloromethyl, and pentafluoroethyl.
The term xe2x80x9carylxe2x80x9d refers to aromatic ring moieties including carboaryls, such as mono- and bicyclic aromatic carbocyclic ring moieties; and heteroaryls, i.e., aromatic ring moieties containing one or more heteroatoms, such as mono- and bicyclic aromatic heterocyclic ring moieties. Aryl groups can be substituted with one or more substituents, such as a halogen, alkenyl, alkyl, alkynyl, hydroxy, amino, thio, alkoxy or cycloalkyl. Exemplary aryls include pyrrole, thiophene, furan, imidazole, pyrazole, 1,2,4-triazole, pyridine, pyrazine, pyrimidine, pyridazine, thiazole, isothiazole, oxazole, isoxazole, s-triazine, benzene, indene, isoindene, benzofuran, dihydrobenzofuran, benzothiophene, indole, 1H-indazole, indoline, azulene, tetrahydroazulene, benzopyrazole, benzoxazole, benzoimidazole, benzothiazole, 1,3-benzodioxole, 1,4-benzodioxan, purine, naphthalene, tetralin, coumarin, chromone, chromene, 1,2-dihydrobenzothiopyran, tetrahydrobenzothiopyran, quinoline, isoquinoline, quinazoline, pyrido[3,4-b]-pyridine, and 1,4-benisoxazine. Preferably, aryl is optionally substituted phenyl, naphthyl, thiophenyl, pyridyl, bi-phenyl, quinolinyl, thiazinyl, isoquinolinyl, imidazolyl, furanyl, fluorenyl, indolyl, or indanyl.
The compounds of the present invention provide a variety of different functional groups upon which further chemical reaction can be performed to generate libraries of compounds. The terms xe2x80x9cadditional synthetic chemistryxe2x80x9d and xe2x80x9cfurther chemical reactionxe2x80x9d are used interchangeably herein to mean one or a series of chemical reactions which are performed to modify or derivatize functional group X. Preferably, additional synthetic chemistry is performed on a resin-bound compound, discussed in detail below, prior to cleavage of the aryl group from the resin-bound compound. Further chemical reactions are selected such that the chemical reactions are compatible with and non-reactive with the aryl silane bond and may be used to prepare derivatives of the aryl compound. It will be recognized by the one skilled in the art that the additional synthetic chemistry performed on the resin-bound compound is done prior to cleavage of the aryl silane bond. Chemical reactions which are compatible with the resin-bound compound include reactions which effectuate the swelling of the polymeric resin thereby allowing penetration of the reagents to react with the functional group X. It should be appreciated that additional synthetic chemistry or further chemical reaction does not include chemical reactions which are reactive with the aryl silane bond. Chemical reaction which cleave the aryl silane bond is herein referred to as a xe2x80x9ccleaving reactionxe2x80x9d to indicate that they cause cleavage of the aryl silane bond. Chemical reagents which are useful in cleaving reactions, i.e., cleaving agent, include acids, fluoride ion sources, electrophiles, and mixtures thereof. Preferably, the cleaving agent is trifluoroacetic acid, HF, pyridinium hydrofluoride, CsF, tetrabutylammonium fluoride, Br2, Cl2, ICl, or mixtures thereof.
The present invention also provides a method for preparing a resin-bound compound comprising coupling a silane compound to a polymeric resin using a transition metal. Preferably, the silane compound comprises an alkenyl moiety, which allows a formation of silylalkylborane compound when the alkenyl moiety is contacted with a hydroborating agent. Preferably, the hydroborating agent is of the formula HBR18R19, where each of R18 and R19 is independently H, C1-C10 or R18 and R19 together form C3-C20 cycloalkyl. Preferred hydroborating agents include 9-BBN, BH3, thexyl borane and other hydrogen containing boranes which are known to one of ordinary skill in the art. More preferably, the silane compound is a compound of formula I above, in which case the resulting resin-bound compound is of the formula: 
where R1, R2, R3, R4, R5, R6, R7, X and Ar1 are those described above; L1 is a bond or a linker preferably L1 is a bond, xe2x80x94Oxe2x80x94, or a moiety of the formula xe2x80x94NHC(xe2x95x90O)xe2x80x94Phxe2x80x94C(xe2x95x90O)NHxe2x80x94CH2xe2x80x94P, where Ph is phenyl; and P is a solid-support. When L1 is a moiety of the formula xe2x80x94NHC(xe2x95x90O)xe2x80x94Phxe2x80x94C(xe2x95x90O)NH-CH2xe2x80x94P, the two amide functional groups can be located on ortho-, meta- or para-position relative to each other, preferably meta or para position, of the phenyl group.
The terms xe2x80x9csolid-support,xe2x80x9d xe2x80x9cresin,xe2x80x9d xe2x80x9cpolymeric resin,xe2x80x9d xe2x80x9cpolymer supportxe2x80x9d and xe2x80x9cpolymeric resin supportxe2x80x9d are used interchangeably to refer to a bead or other solid support such as beads, pellets, disks, capillaries, hollow fibers, needles, solid fibers, cellulose beads, pore-glass beads, silica gels, grafted co-poly beads, polyacrylamide beads, latex beads, dimethylacrylamide beads optionally cross-linked with N,Nxe2x80x2-bis-acryloyl ethylene diamine, glass particles coated with a hydrophobic polymer, etc., i.e., a material having a rigid or semi-rigid surface. The solid support is suitably made of, for example, cross linked polystyrene resin, polyethylene glycol-polystyrene resin, benzyl ester resins or benzhydrylamine resins and any other substance which may be used as such and which would be known or obvious to one of ordinary skill in the art. For purposes herein, it will be obvious to the skilled artisan, that the above terms mean any aliphatic or aromatic polymer which lacks functionality known to participate in the additional synthetic chemistry for generation of the derivatized compounds of this invention, and which is stable to conditions for protodesilylation. Preferred solid-supports for use herein are polystyrene, aminomethylated polystyrene resin, the Tentagel resin, aminomethylated Tentagel resin, polyamide-kieselguhr composites, the Merrifield resin, the Wang resin, and the Rink resin. Preferred polymer resins for use herein are the Merrifield resin (available commercially from Nova Biochem) and the Wang resin (synthesis described below).
In addition, when the silane compound is a compound of formula I above, the silyalkylborane compound which is produced by hydroboration of compound I is of the formula: 
where R1, R2, R3, R4, R5, R6, R7, R18, R19, Ar1, and X are those described above.
The silylalkylborane compound can be coupled to a polymeric resin which includes an aryl halide moiety. In this manner, the coupling reaction results in a formation of a covalent bond between the carbon bonded to the boron atom and the carbon atom of the aryl halide moiety of the polymeric resin which is bonded to the halide. Such coupling can be affected by a transition metal catalyzed coupling reaction which are well known to one of ordinary skill in the art. For example, alkylboranes, including silylalkylboranes, can be coupled to an aryl halide using a palladium catalyzed cross-coupling reaction, which is typically known as the Suzuki reaction. Particular palladium catalysts which are useful in the Suzuki reaction are well known to one of ordinary skill in the art. Alternatively, the silane compound can be converted to a Grignard reagent, e.g., by reaction of an alkyl halide with magnesium metal, and coupled to a solid-support containing an aryl halide moiety by using a transition metal.
The method of the present invention can also include linking the polymeric resin with a linker, e.g., L1 of formula II, which include an aryl halide moiety. Preferably, the linker is of the formula X1xe2x80x94Phxe2x80x94C(xe2x95x90O)OR13, where X1 is a halide, preferably X1 is Cl, Br or I; and R13 is described above. The X1 group of the linker may be located on ortho-, or preferably meta- or para-position relative to the xe2x80x94C(xe2x95x90O)OR13 moiety of the linker.
Alternatively, the silylalkylborane compound can be oxidized to form a silylalkylhydroxy compound prior to the coupling step. Moreover, the hydroxy group of the silylalkylhydroxy compound can be converted to an amine, carboxylate or other functional groups to allow coupling with polymeric resins such as Merrifield. resin, Wang resin, aminomethylated polystyrene resin, Rink resin, and aminomethylated Tentagel resin.
Still yet another embodiment of the present invention provides a method for preparing a library of compounds comprising an aryl group. Methods for generating a library of compounds include:
(a) preparing a plurality of resin-bound compounds;
(b) optionally dividing the resin-bound compounds into a plurality of portions;
(c) performing additional synthetic chemistry to modify the functional group X to produce modified resin-bound compounds;
(d) optionally recombining the portions; and
(e) cleaving at least a portion of the modified resin-bound compounds from the polymeric resin supports so that the aryl groups resulting from the cleavage have a hydrogen, halide, hydroxy or acyloxy group on the aryl carbon atom which were bound to the polymeric resin through the silyl group.
The steps of (b) dividing resin-bound compounds, (c) performing additional synthetic chemistry, and (d) combining the portions can be repeated as many times as desired to generate larger compounds.
The compounds (or libraries of compounds) made by the instant methods may either remain bound to the resin which is used to perform the resin-bound synthesis (hereinafter referred to as xe2x80x9cresin-bound compounds (or libraries)xe2x80x9d) or not bound to a resin (hereinafter referred to as xe2x80x9csoluble compounds (or libraries)xe2x80x9d). For example, the resin-bound compounds can be cleaved from the polymeric resin support by treatment with a cleaving agent including an acid, a fluoride ion source, an electrophile, and mixtures thereof. Thus, the cleaved compounds can have a hydrogen, halogen, hydroxy or acyloxy group bound to the aryl carbon atom which was bound to the silyl group after cleavage from the solid-support. Preferably, the cleaving agent is trifluoroacetic acid, HF, pyridinium hydrofluoride, CsF, tetrabutylammonium fluoride, Br2, Cl2, ICl, or mixtures thereof.
The terms xe2x80x9cresin-bound synthesisxe2x80x9d and xe2x80x9csolid phase synthesisxe2x80x9d are used herein interchangeably to mean one or a series of chemical reactions used to prepare either a single compound or a library of molecularly diverse compounds, where the chemical reactions are performed on a compound, which is bound to a polymeric resin support.
Based upon the disclosure herein, it will be clear to one of ordinary skill in the art that there are many possible synthetic approaches to creating the libraries of this invention. The libraries can be prepared on a solid support, e.g., a resin, or they can be prepared in solution. For example, the variable substituents can be added by reacting core structure, labeled R, with a mixture of reagents designed to introduce substituents X1xe2x88x92m collectively or by reacting aliquots of R with individual reagents each one of which will introduce a single substituent Ri and then mixing the resultant products together (wherein i, j and k are used herein to represent any of the substituents on the compound members of the combinatorial library).
For reasons of efficiency, the components of the library are screened in groups of multiple compounds. Therefore, once the library of compounds has been synthesized, there must be some method to deconvolute the results of screening such that individual active compounds can be identified. Based upon the disclosure herein, it will be clear to one of ordinary skill in the art that there are many methods for deconvolution of the combinatorial library. For example, if the compounds of the library are screened on a solid support, they may be physically segregated so that individual active compounds may be directly selected and identified. In contrast, if the compounds of the library are tested as soluble mixtures, e.g., after cleaving from the solid-support, the library may be deconvoluted in an iterative approach, which involves resynthesis of mixtures of decreasing complexity until a single compound is identified, or in a scanning approach, in which the various substituents on the core structure, are evaluated independently and the structure of active compounds are determined deductively.
In its simplest form, the iterative approach to deconvoluting the combinatorial library involves separation of the combinatorial library of compounds immediately prior to the introduction of the last variable substituent. Using the same nomenclature, i.e., R is the core structure, etc., as used above, the mixture of compounds RX1xe2x88x92mY1xe2x88x92n is partitioned into p aliquots (wherein m, n and p are integers which define the size of the library, and which range between 1 to 1000; preferably between 1 to 100, most preferably between 1 to 20). Each of those aliquots is reacted with reagents designed to introduce a single substituent, labeled Z. Thus, p different pools RX1xe2x88x92mY1xe2x88x92nZi, each of which contains (mxc3x97n) compounds with all possible variations of X and Y being represented but only one particular Z, will be obtained. Screening this library in a binding or functional assay defines the appropriate Z substituent(s) for the desired activity. The term xe2x80x9cassayxe2x80x9d refers to a binding assay or a functional assay known or obvious to one of ordinary skill in the art for a particular purpose.
Once the appropriate Z substituent, labeled Za, is determined (for illustrative purposes, only one active compound exists, however, it would be clear to one of ordinary skill in the art that more than one active compound may exist in the library), the library is prepared again, this time splitting the mixture of compounds RX1xe2x88x92m into n aliquots for introduction of the n different Y substituents (as used herein xe2x80x9caxe2x80x9d, xe2x80x9cbxe2x80x9d and xe2x80x9ccxe2x80x9d refer to specific acceptable substituents which have been determined to be active by screening in a binding or functional assay). After the Y substituents are introduced, the Za substituent is introduced into each of the still separated aliquots. The library now consists of n pools RX1xe2x88x92mYjZa, each of which contains m different compounds with all the possible X substituents. represented, and one particular Y substituent. Screening this library in a binding or functional assay defines the appropriate Y substituent, labeled Yb.
In a similar manner, the appropriate X substituent, labeled Xc is determined by beginning with m different aliquots of core structure R and sequentially introducing Xk, Yb and Za to give m different pools RXkYbZa, each of which contains a single compound. Thus only m+n+p syntheses are required to deconvolute a library containing (mxc3x97nxc3x97p) compounds.
The iterative approach is specific for a single target which is determined after the first round of screening, since subsequent library preparations do not contain the full complement of substituents.
The application of the scanning approach to deconvoluting the combinatorial library requires that the variable substituents X, Y and Z can be introduced synthetically independently of each other. The library is first prepared as RX1xe2x88x92mY1xe2x88x92nZi exactly as in the iterative approach to give p pools RX1xe2x88x92mY1xe2x88x92nZi, each of which contains (mxc3x97n) compounds with all possible variation of X and Y represented but only one particular Z. Screening this library defines the appropriate Z substituents for the desired activity.
Since Y can be introduced independently from X and Z, the library is then prepared as RX1xe2x88x92mYjZ1xe2x88x92p, giving n pools of compounds each containing (mxc3x97p) compounds in which all substituents X and Z are represented with a particular Y substituent. Screening this library in a binding or functional assay defines the appropriate Y substituents for the desired activity.
Since X can also be introduced independently from Y and Z, the library is then prepared as RXkY1xe2x88x92nZ1xe2x88x92p, giving m batches or pools of compounds, each of which contains (nxc3x97p) compounds in which all substituents Y and Z are represented with a particular X substituent. Screening this library in a binding or functional assay defines the appropriate X substituents for the desired activity. The terms xe2x80x9cbatchesxe2x80x9d or xe2x80x9cpoolsxe2x80x9d are used interchangeably and refer to a collection of compounds or compound intermediates.
In the simplest case, a single X, Y and Z substituent are identified from the three libraries, thus converging on a single compound RXcYbZa. The advantage of utilizing the scanning approach is that each library contains all the possible permutations of X, Y and Z and can be utilized to screen against a number of different biological targets.
Compounds of the present invention may be useful in a variety of applications including in a synthesis of other organic chemicals, including xcex1- and xcex2-amino acids, peptides, such as sansalvamide, leualacin, astin G, pristinamycin I and lissoclinum cyclopeptides; and as receptor ligands, including aspartyl protease inhibitors (such as HIV protease, renin, and cathepsins D and E), farnesyltransferase inhibitors, cyclooxygenase (COX-2) inhibitors, GP IIbIIIa antagonists, and ligands to somatostatin receptors. Suitable assays for identifying or determining a ligand for a particular receptor are well known to one of ordinary skill in the art. Thus, compounds prepared by the methods described herein can be screened in assays developed for determining lead compound as pharmaceutical agents.
The resin-bound compounds of the present invention provide several different functional groups upon which allows further chemical reactions to generate libraries of compounds. A variety of drugs and/or biologically active agents, in particular compounds containing a bulky hydrophobic moiety, can be synthesized on the solid-support using the compounds and methods described herein, including xcex1- and xcex2-amino acids attached to the solid-support through its aromatic side chain by silyl linkage, silylated-aromatics with various functional groups such as bromo-, hydroxy-, and amino-alkyl, formyl, carboxylic acid. In particular, phenylalanine-containing dipeptide analogs, xcex2-homophenylalanine-containing tripeptide analogs, benzyl or phenethyl-containing secondary amines, benzyl substituted sulfonamides, N-benzylated peptidomimetics can be synthesized on the solid-support in high yield and purity.
The compounds of the present invention can be synthesized from readily available starting materials. Various substituents on the compounds of the present invention can be present in the starting compounds, added to any one of the intermediates or added after formation of the final products by known methods of substitution or conversion reactions. If the substituents themselves are reactive, then the substituents can themselves be protected according to the techniques known in the art. A variety of protecting groups are known in the art, and can be employed. Examples of many of the possible groups can be found in Protective Groups in Organic Synthesis, 3rd edition, T. W. Greene and P. G. M. Wuts, John Wiley and Sons, New York, 1999, which is incorporated herein by reference in its entirety. For example, nitro groups can be added by nitration and the nitro group can be converted to other groups, such as amino by reduction, and halogen by diazotization of the amino group and replacement of the diazo group with halogen. Acyl groups can be added by Friedel-Crafts acylation. The acyl groups can then be transformed to the corresponding alkyl groups by various methods, including the Wolff-Kishner reduction and Clemmenson reduction. Amino groups can be alkylated to form mono- and di-alkylamino groups and mercapto and hydroxy groups can be alkylated to form corresponding ethers. Primary alcohols can be oxidized by oxidizing agents known in the art to form carboxylic acids or aldehydes, and secondary alcohols can be oxidized to form ketones. Thus, substitution or alteration reactions can be employed to provide a variety of substituents throughout the molecule of the starting material, intermediates, or the final product including isolated products.
Since the compounds of the present invention can have certain substituents which are necessarily present, the introduction of each substituent is, of course, dependent on the specific substituents involved and the chemistry necessary for their formation. Thus, consideration of how one substituent would be affected by a chemical reaction when forming a second substituent would involve techniques familiar to one of ordinary skill in the art.
It is to be understood that the scope of this invention encompasses not only the various isomers which may exist but also the various mixture of isomers which may be formed.
If the compound of the present invention contains one or more chiral centers, the compound can be synthesized enantioselectively or a mixture of enantiomers and/or diastereomers can be prepared and separated. The resolution of the compounds of the present invention, their starting materials and/or the intermediates may be carried out by known procedures, e.g., as described in the four volume compendium Optical Resolution Procedures for Chemical Compounds: Optical Resolution Information Center, Manhattan College, Riverdale, N.Y., and in Enantiomers, Racemates and Resolutions, Jean Jacques, Andre Collet and Samuel H. Wilen; John Wiley and Sons, Inc., New York, 1981, which are incorporated herein by reference in their entirety. Basically, the resolution of the compounds is based on the differences in the physical properties of diastereomers by attachment, either chemically or enzymatically, of an enantiomerically pure moiety results in forms that are separable by fractional crystallization, distillation or chromatography.
When the compound of the present invention contains an olefin moiety and such olefin moiety can be either cis- or trans-configuration, the compound can be synthesized to produce cis- or trans-olefin, selectively, as the predominant product. Alternatively, the compound containing an olefin moiety can be produced as a mixture of cis- and trans-olefins and separated using known procedures, for example, by chromatography as described in W. K. Chan, et al., J. Am. Chem. Soc., 1974, 96, 3642, which is incorporated herein in its entirety.
For all of the following Schemes, standard work-up and purification methods can be used and will be obvious to one of ordinary skill in the art. In addition, it will be recognized that the aryl group coupled to the polymer resins through the silyl group illustrated below, can be optionally substituted at any appropriate site, depending upon the type of derivatization required. 
One method for preparing a representative compound of the present invention, i.e., 4-allyldimethylsilylbenzyl alcohol (3 Scheme 1) is shown in Scheme 1. As used herein, the term xe2x80x9c(x Scheme y)xe2x80x9d refers to compound number x in Scheme Y. A metal-halogen exchange reaction of the starting 1,4-dibromobenzene with n-butyllithium followed by addition of allylchlorodimethylsilane produces aryl sliane (1 Scheme 1). Treatment of (1 Scheme 1) with magnesium in THF generated Grignard reagent which was reacted with paraformaldehyde to afford (3 Scheme 1). Alternatively, reaction of (1 Scheme 1) with t-butyllithium followed by quenching with anhydrous DMF produced 4-allyldimethylsilylbenzaldehyde (2 Scheme 1). Reduction of 4-allyldimethylsilylbenzaldehyde with sodium borohydride gave (3 Scheme 1).
Alternatively, protection of 4-bromobenzyl alcohol (4 Scheme 1) with THP, followed by lithium-halogen exchange with n-butyllithium and treatment with allylchlorodimethylsilane afforded the arylsilane (6 Scheme 1). Removal of the THP group with TsOH gave 4-allyldimethylsilylbenzyl alcohol (3 Scheme 1).
Conventional solid-phase peptide synthesis allows the elongation of the amino acid backbone in unidirection (C to N or N to C). A more efficient approach to the synthesis of peptides involves the anchoring of the side chain to the polymer, an approach that has been utilized, especially for head-to-tail cyclization of cyclic peptides. This methodology provides minimal risks for side reactions, such as dimerization and oligomerization, even under reaction conditions of high concentration. Furthermore, this side-chain anchoring strategy allows the generation of more diverse libraries of compounds than the conventional unidirectional methods. This bi-directional functionalization is especially applicable for preparing compounds whose C- and N-terminals are both capped with non-amino acids. Because the conventional linkers are mainly based on the polar functional groups, this method has been applicable only to amino acids which have polar side chains such as Asp, Glu (COOH); Ser, Tyr (OH); Lys (NH2); or His (imidazole). For the amino acids which have a hydrophobic aliphatic or aromatic carbon chain, a side chain anchoring strategy for solid phase synthesis has not been reported.
Because of the non-polar nature and steric bulkiness of its side chain, phenylalanine is one of the preferred residues in peptidomimetics for favorable interaction with biological targets. Almost every aspartyl protease, such as HIV protease, renin, cathepsins D and E, has a preference for hydrophobic amino acid side chains at the P1 position; consequently, peptidomimetics designed to inhibit these enzymes generally contain phenylalanine mimics or other bulky hydrophobic groups at P1 position. A large number of naturally occurring linear peptides with antineoplastic activity, such as Dolastatin 10 and 15, and numerous cyclic peptides that are hydrophobic also contain at least one phenylalanine residue.
As shown in Schemes 2-4, the present invention provides one of the most efficient methods for producing a library of phenylalanine-containing molecules by providing a resin-bound compounds in which the phenylalanine side chain is attached to the polymer support, thus allowing both the N- and C-termini to be varied independently. 
Bromination of 4-allyldimethylsilylbenzyl alcohol (3 Scheme 1) was carried out with triphenylphosphine and carbon tetrabromide. To insure high diastereoselectivity of the product, carbon-carbon bond formation between the benzyl bromide (1 Scheme 2) and lithiated bislactim ether was performed by a slow addition of benzyl bromide (1 Scheme 2) in dry THF to the lithiated bislactim ether stirred at xe2x88x9278xc2x0 C. in THF. This amino acid precursor with an allyldimethysilyl functional group was linked to the polymer by two step sequences. Hydroboration of the allylsilane (2 Scheme 2) with 9-BBN followed by in situ Suzuki coupling with bromopolystyrene provided a resin bound phenylalanine derivative (3 Scheme 2). Treatment of the resin with a solution of THY/1N HCl (8:1) for 3 h at room temperature afforded phenylalanine ethyl ester (4 Scheme 2) which is ready for further derivatization on a polymer support.
Alternatively, the bislactim ether (2 Scheme 2) was hydrolyzed under mild acidic conditions to obtain the amine which was protected as an N-Fmoc carbamate (5 Scheme 2) or N-Boc carbamate (7 Scheme 2). The same coupling conditions as described above provided the resin bound phenylalanine derivatives (6 Scheme 2) and (8 Scheme 2), respectively. The loading level of the amino acid derivatives bound to the polymer was determined by the Fmoc release UV/VIS assay or by mass balance of the corresponding bromo analog released from the resin after brief treatment of the resin with Br2 in dichloromethane. 
As illustrated in Scheme 3, to extend the N-terminal of (6 Scheme 2), Fmoc group was removed, the free amide group was coupled with benzoic acid, the resulting product was treated with LiOH (5 eq) in THF/H2O (8:1) for 3 h at room temperature. Cleavage of the compound was carried out with Br2 to release the ester (1 Scheme 3). The ester can be hydrolyzed by heating in the presence of LiOH. 
The utility of the polymer bound phenylalanine precursor is demonstrated by the preparation dipeptide analogues from both the N- and C-termini as shown in Scheme 4. Deprotection of Fmoc group followed by coupling with benzoic acid gave an N-benzoyl amide. Hydrolysis of the ester was carried out under the standard hydrolysis conditions (i.e., LIOH (5 eq) in THF/H2O (8:1) for 1 h at 75xc2x0 C.), then the C-terminal coupling was performed on this carboxylic acid with glycine methyl ester. The dipeptide analogue was cleaved from the resin with 50% TFA to yield protected dipeptide (1a Scheme 4). Alternatively, cleavage of the dipeptides from the resin by ipso-substitution of the silyl group with electrophiles (Br2 or ICl) gave the corresponding halogen-substituted compounds (1b Scheme 4 and 1c Scheme 4).
Similarly, but in a reverse reaction sequence, the same compound (1a Scheme 4) was synthesized on the solid support starting from the N-Boc-protected phenylalanine precursor (6 Scheme 2). C-terminal amide coupling with glycine methyl ester followed by deprotection of the Boc group with 50% TFA, and subsequent coupling with benzoic acid, afforded dipeptide (1a Scheme 4) after cleavage from the resin. The polymer-bound phenylalanine can be modified in either the N- or C-terminal direction with readily available reagents, such as amines and carboxylates, and diversity can be further increased by cleaving the peptide from the resin with halogens to give para-substituted halophenylalanines. These halogenated analogues can be further elaborated by variety of alkyl or aryl substitution reactions at the halide.
This method can be applied to cyclic peptide synthesis by head-to-tail cyclization of a peptide on a solid support.
The arylsilyl linkage in the compounds of the present invention is generally resistant to moderate acidic [1 N HCl/THF (1:8); 50% TFA/CH2Cl2 for 10 min] and basic conditions [LiOH, THF/H2O (8:1), heat] as well as to the general amide coupling reactions. 
Another method for preparing a resin-bound phenylalanine derivative is shown in Scheme 5. Tetramethylguanidine-mediated Horner-Emmons olefination reaction of 4-allyldimethylsilylbenzaldehyde (2 Scheme 1) with methyl-2-acetylamido-2-(dimethoxyphosphinyl)-acetate gave (Z) xcex1-eneamide ester (1 Scheme 5). Asymmetric catalytic hydrogenation reaction of xcex1-eneamide ester gave the xcex1-chiral amino acid precursor (2 Scheme 5). N-acetyl group was converted to Boc protecting group by treatment with di-tert-butyl dicarbonate followed by excess hydrazine in one-pot procedure to afford the desired product (3 Scheme 5). Hydroboration and Suzuki coupling reaction of the Boc-protected phenylalanine methyl ester (3 Scheme 5) produced the polymer-bound phenylalanine derivative (4 Scheme 5). 
As shown in Scheme 6, the same reaction sequence illustrated in Scheme 5 can be applied to other arylsilyl-derived aldehydes to generate chiral amino acids with various silylated aromatic side chain.
Thus, 2-allyldimethylsilylthiophene-5-carboxaldehyde (1 Scheme 6), 1-allyldimethylsilyl-4-naphthaldehyde (5 Scheme 6), and 4-allyldimethylsilylphenylacetaldehyde (9 Scheme 6) underwent the following sequential reactions; Horner-Emmons olefmation, asymmetric catalytic hydrogenation reaction, and one-pot conversion of acetyl group to Boc protecting group, to give silylated-thienylalanine (4 Scheme 6), naphthylalanine (8 Scheme 6), and phenethylglycine analogue (12 Scheme 6), respectively. Hydroboration and Suzuki coupling reaction of these compound then yields corresponding products. 
HIV protease inhibitors, along with reverse transcriptase inhibitor drugs, are important components of a cocktail used for treating patients with AIDS. Inhibitors of HIV protease can be accessed by the incorporation of an isostere that mimics the geometry of the tetrahedral intermediate in place of the scissile bond of the peptide substrate. Many potent inhibitors have been developed using this principle. One of the structures identified effective for inhibition of HIV protease is the hydroxyethylamine isostere where a secondary alcohol mimics a stable tetrahedral intermediate in the region spanning P1-P1xe2x80x2. In fact, several approved HIV protease drugs on the market and drug candidates are based on the hydroxyethylamine isostere as a key pharmacophore. A different type of HIV protease inhibitors containing cis-epoxide are also known. One of the structural features the known HIV protease inhibitors share in common is that the key pharmacophore is derived from phenylalanine (or phenylalanine analogs), indicating that the bulky hydrophobic residue in these inhibitors may be important for their biological activities. The present invention provides compounds which can be used for solid-phase synthesis of HIV protease inhibitors and method for preparing the same. Compounds of the present invention can also be adapted as tools for synthesis of other aspartyl protease inhibitors.
Two silylated intermediates (2 Scheme 7 and 4 Scheme 7) which are well-known precursors of HIV protease inhibitors were prepared as shown in Scheme 7. Reduction of N-acetyl amino ester (2 Scheme 5) gave an aldehyde (1 Scheme 7) which underwent Wittig olefination reaction to produce a disubstituted cis-double bond (2 Scheme 7). Once this compound was attached to the polymer via the coupling reaction as described in Scheme 2, the polymer bound building block could be used for rapid synthesis of irreversible HIV protease inhibitors containing phenylalanine-derived cis-epoxide.
Butadiene diepoxide react with Grignard reagent at the less hindered carbon. Azidation of the resulting alcohol (3 Scheme 7) under Mitsunobu conditions provided the desired azido oxirane derivative (4 Scheme 7). After an appropriate modification of azide function followed by coupling to the polymer, the resin-bound compound can be used for parallel (or combinatorial) synthesis of aspartyl protease inhibitors. 
Phenylglycine is an important component of many natural products. One of the phenylglycine containing cyclic peptides of biological significance is the family of pristinamycin I. Pristinamycin I, along with its other synergistic component pristinamycin II, is used for the treatment of infection. Pristinamycin I is a mixture of three peptidic macrolactones: pristinamycin IA, IB, and IC, which differ by one methyl group. It is composed of six amino acid residues which are connected with five amide bonds and one ester bond. The amino group of the threonine residue is acylated with 3-hydroxy picolinic acid. The successful synthetic approaches of pristinamycin I involves construction of a linear ring-opened depsipeptide and subsequent ring closure by formation of an amide ring.
Due to the limitation of currently available linkers for solid phase synthesis, cyclic compounds such as pristinamycin I, which do not have any polar side chains, are not suitable for a head-to-tail cyclization strategy on a solid support. Compounds of the present invention include resin-bound phenylglycine derivatives which can be used for solid-phase synthesis of Pristinamycin I as well as other phanylglycine-containing cyclic compounds.
Preparation of phenylglycine derivative with a silyl group attached to the phenyl ring is shown in Scheme 8. 4-allyldimethylsilylphenethyl alcohol (1 Scheme 8) was oxidized to produce 4-allyldimethylphenylacetic acid (2 Scheme 8). This acid was activated with pivaloyl chloride and treated with a lithiated chiral oxazolidinone to obtain an imidate (3 Scheme 8). Evans asymmetric azidation reaction gave azido imidate (4 Scheme 8). Treating the purified isomer (4 Scheme 8) with titanium mediated esterification reaction gave a methyl ester (5 Scheme 8) which was treated with trimethylphosphine followed by BocON in one pot to obtain Boc-protected phenylglycine methyl ester (6 Scheme 8). This was attached to the polymer by hydroboration and Suzuki coupling reaction to generate polymer-bound phenylglycine derivative (7 Scheme 8). Deprotection of Boc group and acylation of the resulting amine with benzoic acid, then subsequent cleavage with bromine released bromo-substituted analog (8 Scheme 8). The polymer-bound phenylglycine derivative (7 Scheme 8) can be used for solid-phase synthesis of pristinamycin I and other phenylglycine-containing peptides of biological importance. 
If the libraries of target molecules require aromatic side chain not the amino acid back bone as an essential element for favorable interactions with biological entity of interest, the xcex1-amino acid can be replaced with other type of multi-functional unit, such as xcex2-amino acids. Therefore, new amino acid building blocks can be designed to generate libraries of compounds containing an aryl side chain. As an example, cyclo xcex2-tetrapeptide prepared as somatostatine analog by others was found to display a significant biological activity and affinity for human receptors. In fact, various xcex2-amino acid compounds may be used for the design of therapeutic agents with improved oral bioavailability.
Moreover, xcex2-amino acids are important components of numerous natural products and therapeutic agents. Because of the enzymatic stability of xcex2-peptides in the biological systems, xcex2-amino acids have become useful building blocks for the design of new peptidomimetics. Consequently, there has been growing demand for xcex2-amino acids. Although several known methods, for example, Arndt-Eistert homologation of xcex1-amino acids and catalytic hydrogenation of 3-amino acrylate, are widely used for the preparation of xcex2-amino acids, and a number of xcex2-amino acids are commercially available, it is highly desirable to develop a new methodology for polymer bound xcex2-amino acids building block as a tool for rapid synthesis and high diversification of compounds.
The synthetic procedure for the preparation of xcex2-amino acid attached to the polymer through its side chain is outlined in Scheme 9. Condensation of 4-allyldimethylsilylbenzaldehyde (2 Scheme 1) with (R)-(xe2x88x92)-tert-butanesulfinamide in the presence of titanium propoxide gave tert-butanesulfinyl imine (1 Scheme 9).
The titanium enolate generated by transmetalation of lithiated methyl acetate with TiCl(O-i-Pr)3 was reacted with imine (1 Scheme 9) to provide a sulfinylated xcex2-amino ester (2 Scheme 9). The diastereoselectivity of xcex2-amino ester (2 Scheme 9) was determined by the analysis of the Mosher amide (3 Scheme 9), prepared by deprotection of the tert-butanesulfinyl group followed by subsequent derivatization of amino group with (R)-(xe2x88x92)-xcex1-methoxy-xcex1-(trifluoromethyl)-phenylacetic acid chloride (MTPACl). Analysis of both 1H NMR and 19F NMR spectra of Mosher amide (3 Scheme 9) showed less than 1% of the minor diastereomer. Hydroboration of the terminal olefin of xcex2-amino ester (2 Scheme 9) followed by in situ Suzuki coupling with bromopolystyrene resin resulted in polymer-bound xcex2-amino acid derivative (4 Scheme 9). The loading level (0.32 mequiv/g) of resin (4 Scheme 9) can be determined by mass balance of (3R)-methyl 3-amino-3-(4-bromophenyl)-butyrate (5 Scheme 9) which can be obtained by stirring an aliquot of resin (4 Scheme 9) with 50% TFA in CH2Cl2 for 5 min followed by washing and cleavage reaction (Br2, CH2Cl2, 20 min). 
Scheme 10 illustrates the suitability of compounds of the present invention (4 Scheme 9) in a wide variety of solid-phase organic synthesis, including synthesis of tripeptides (2 Scheme 10). The resin-bound compound (4 Scheme 9) was treated with 50% TFA to remove tert-butanesulfinyl group. The resulting amino group was reacted with Fmoc-Ala-OH using standard EDC and HOBt coupling conditions in DMF, then Fmoc group was deprotected with 20% piperidine in DMF. After several washings of the resin, benzoic acid was coupled to the amine to yield polymer-bound dipeptide analog (1 Scheme 10). Hydrolysis of the ester group at the C-terminus of resin (1 Scheme 10) with LiOH(5 eq.) in THF/H2O (8:1) under refluxing condition for 2.5 h, coupling with Gly-OEt, and cleavage of the product with TFA gave tripeptide (2a Scheme 10).
Alternatively, cleavage of the tripeptide from the resin by ipso-substitution of the silyl group with Br2 gave bromo-substituted tripeptide (2b Scheme 10). Likewise, cleavage of the tripeptide with ICl gave iodo-substituted tripeptide (2c Scheme 10).
Because non-polar aromatic rings play important roles as a pharmacophore in bioactive molecules, compounds of the present invention may be used for the design of focused library containing xcex2-amino acid with a non-polar aryl side chain. 
A similar approach as illustrated in Scheme 9 was employed to prepare a silylated compound (1 Scheme 11) which can be used for the synthesis of other biologically active compounds. 4-allyldimethylsilylphenylacetaldehyde (9 Scheme 6) was condensed with (R)-(xe2x88x92)-tert-butanesulfinamide to give tert-butanesulfinyl imine (1 Scheme 11). Reaction of the resulting compound with appropriate Grignard reagents provides important intermediates which are useful for a synthesis of irreversible HIV protease inhibitors.
By following the same reaction sequence as described in Scheme 9, the imine (1 Scheme 11) can also be converted to a xcex2-amino acid compound which can be linked (i.e., attached) to a solid support. 
Hydroboration of the double bond and subsequent Suzuki coupling of the resulting organoborane to the bromopolystyrene was utilized as a preferred method to attach the compounds of the present invention to a solid support. Because organoboranes can be efficiently replaced by hydroxyl, halogen, or amino groups by well established chemistry, other polystyrene resins may be used to attach properly functionalized compounds of the present invention. As illustrated in Scheme 12, treatment of silylated bislactim ether (2 Scheme 2) with 9-BBN followed by alkaline hydrogen peroxide gave a primary alcohol (1 Scheme 12). In the similar manner, silylated phenylglycine precursor (5 Scheme 8) can be converted to the corresponding alcohol derivative (2 Scheme 12). Appropriate reactions for linking these alcohol functionalized compounds to a variety of polymer resins (e.g., Merrifield, Wang, and hydroxymethyl polystyrene resins) are well known to one of ordinary skill in the art. 
Preparation of other useful organic compounds using the processes of the present invention is illustrated in Scheme 13. For example, 4-allyldimethylsilylbenzyl alcohol (3 Scheme 1) was attached to the bromopolystyrene resin by two step sequences. Hydroboration of the allylsilane with 9-BBN followed by in situ Suzuki coupling with bromopolystyrene provided a polymer-bound benzylalcohol (1 Scheme 13). Polymer-bound benzyl bromide (2 Scheme 13) was readily prepared from polymer-bound benzyl alcohol (1 Scheme 13). Treatment of polymer-bound benzyl bromide (2 Scheme 13) with Br2 gave 4-bromobenzyl bromide. The loading level of resin (2 Scheme 13, 0.37 mequiv/g) was determined by mass balance of the obtained 4-bromobenzyl bromide. As will be obvious in the following examples, these two polymer-bound compounds (1 Scheme 13, and 2 Scheme 13) can be used for immobilization of appropriate carboxylic acids, amines, and alcohols.
Reaction of 4-allyldimethylsilylbenzyl alcohol (3 Scheme 1) with triphenylphosphine and carbon tetrabromide gave 4-allyldimethylsilylbenzyl bromide (4 Scheme 13). Subsequent reaction with potassium cyanide gave 4-allyldimethylsilylphenylacetonitrile (6 Scheme 13). Under the usual coupling conditions, this was loaded to the polymer and the loading level of resin (2 Scheme 13, 0.23 mequiv/g) was determined by the mass balance of 4-bromophenylacetonitrile which was obtained from cleavage reaction of the resin with bromine. 
Polymer support functionalized with hydroxyl group, such as Wang and hydroxymethyl polystyrene, can be used for the immobilization (i.e., linking) of alcohols, carboxylic acids, and amines. Scheme 14 shows modification (i.e., chemical transformation) of polymer-bound alcohol (1 Scheme 13) to provide new polymer-bound compounds. Etherification of 4-hydroxybenzaldehyde with polymer-bound benzyl alcohol (1 Scheme 13) under Mitsunobu condition gave polymer-bound benzyloxybenzaldehyde (1 Scheme 14) which was identified by isolation of 4-(4-bromobenzyloxy)benzaldehyde (2 Scheme 14).
Selective alkylation of 4-hydroxybenzyl alcohol with 4-allyldimethylsilylbenzyl bromide (4 Scheme 13) gave 4-(4-allyldimethylsilylbenzyloxy)benzyl alcohol (3 Scheme 14) which was linked to bromopolystyrene to provide polymer-bound benzyloxybenzyl alcohol (4 Scheme 14). Functional group transformation of alcohol to bromide on the polymer support gave polymer-bound benzyloxybenzyl bromide (5 Scheme 14). 
Numerous pharmaceutical agents are derivatized with non-polar aryl moieties, which limit solid-phase synthesis approach using conventional solid-support synthesis. For example, the N-substituted dipeptide analog (1 Scheme 15) was found to have anti-tumor activity. Because both of N- and C-termini of the dipeptide (1 Scheme 15) are derivatized with non-polar aromatic groups, solid-phase synthesis and combinatorial approach of these analogs using conventional solid support is difficult.
A reasonable retrosynthetic analysis for solution reaction dissects this molecule (1 Scheme 15) to three parts, Cbz-protected histidine (2 Scheme 15), secondary amino ester (3 Scheme 15), and a primary amine (4 Scheme 15). The secondary amino ester can be further dissected to 4-(benzyloxy)benzaldehyde (5 Scheme 15) and glycine ethyl ester. Standard peptide coupling reactions could put them together to give the dipeptide (1 Scheme 15) derivatized with non-polar aromatic rings. It was found that the polymer-bound compounds (1 Scheme 14 and 5 Scheme 14) prepared in Scheme 14 can be used for a solid-phase synthesis of this molecule. Polymer-bound benzyloxybenzylbromide (5 Scheme 14) reacts with glycine ethyl ester to produce a secondary amino ester (6 Scheme 15).
Alternatively, reductive am ination of polymer-bound benzyloxybenzaldehyde (1 Scheme 14) with glycine ethyl ester can provide the same polymer-bound secondary amino ester which can be subjected to a peptide coupling as described above for solution reactions. 
Scheme 16 illustrates compounds and methods of the present invention which allow retaining a benzyl functional group after cleavage from the solid-support. Various carboxylic acids (or amino acids) can be attached to the resin-bound compound (3 Scheme 16) under the typical amide coupling conditions to yield a resin-bound amide (4 Scheme 16) and later cleaved from the solid-support to give a compound with a benzyl moiety which has a non-polar functionality such as H, Br, or I on the phenyl ring. Carboxylic acids with other functional group can be subjected to a variety of other chemicals reaction to modify the functional group. For example, malonic acid derivatives bound to the benzylamine linker can be subjected to a Knoevenagel reaction to generate 1,3-carbonyl derivatives. Imines formed from condensation reaction with aldehydes can be treated with Grignard reagents (alkyl- or aryllithium) to give various xcex1-branched secondary amines or used for the synthesis of xcex2-lactams via [2+2] Staudinger reaction on solid support. In situ reduction [NaBH(OAc)3, CH2Cl2] of the imines yields polymer-bound secondary amines which can be further derivatized, e.g., to benzyl group-containing carboxamides or sulfonamides.
The polymer-bound silylated benzylamine (3 Scheme 16) can be prepared according to the procedure illustrated in Scheme 16. Mitsunobu reaction of 4-allyldimethylsilylbenzyl alcohol (3 Scheme 1) with N-Boc protected ethyl oxamate followed by hydrolysis afforded Boc-protected silylated benzylamine (2 Scheme 16). Hydroboration with 9-BBN followed by Suzuki coupling with bromopolystyrene provided polymer-bound N-Boc protected benzylamine (3 Scheme 16).
Standard peptide coupling reaction using this polymer-bound benzylamine (3 Scheme 16), with either Boc or Fmoc protecting group, and appropriate carboxylic acids gave benzylamine-containing dipeptide analog (5 Scheme 16). 
The applications of the polymer-bound benzylbromide (2 Scheme 13) for solid-phase synthesis of small organic molecules are illustrated in Scheme 17. In order to synthesize a secondary amine, the polymer-bound benzylbromide (2 Scheme 13) was reacted phenethylamine followed by cleavage of the solid-support to obtain the desired secondary amine (2 Scheme 17).
In solution chemistry, reaction of alkyl halides with primary amines results in a mixture of mono- and dialkylated products. However, reaction of excess primary amine with resin-bound alkylating agent provided only a secondary amine (1 Scheme 17). The resin-bound secondary amine (1 Scheme 17) was further reacted with p-toluenesulfonyl chloride to give sulfonamide (3 Scheme 17) after cleavage reaction.
Treatment of the polymer-bound benzylbromide (2 Scheme 13) with Gly-OEt, followed by sulfonamide formation with p-toluenesulfonyl chloride, hydrolysis of intermediate ester under the alkaline conditions, treatment with O-ethyl hydroxylamine under the coupling conditions, and cleavage from the solid-support with bromine gave a hydroxamic acid analog (4 Scheme 17). This class of hydroxamic acid analogs is a known inhibitor of matrix metalloproteinase (MMP) which have become important pharmacological targets for treatment of many diseases.
Instead of sulfonylation of the secondary amine intermediate, peptide coupling with amino acid gave N-benzylated peptidomimetics. Efficient synthesis of this type of compounds is important for the design of peptide analogs with favorable in vivo activity. Thus, a peptidomimetic with increased hydrophobic nature, N-benzylated peptide analog (5 Scheme 17) was synthesized using the polymer-bound benzylbromide (2 Scheme 13). The secondary amine intermediate formed from the reaction with the polymer-bound benzylbromide (2 Scheme 13) and glycine ethyl ester was coupled with Fmoc protected xcex2-alanine acid fluoride. Deprotection of Fmoc group by treatment of the resin with 20% piperidine afforded a free amine which was acylated by the subsequent coupling reaction with benzoic acid. Cleavage reaction with bromine yielded the desired peptide analog (5 Scheme 17). 
The synthetic procedure for preparation of polymer-bound benzaldehyde (5 Scheme 18) is illustrated in Scheme 18. 4-Bomobenzaldehyde (1 Scheme 18) was protected to 1,3-dioxolane derivative (2 Scheme 18). Lithium-halogen exchange of (2 Scheme 18) with t-butyllithium followed by addition of allydimethylsilyl chloride gave 2-(4-allyldimethylsilylphenyl)-1,3-dioxolane (3 Scheme 18). Hydroboration of (3 Scheme 18) with 9-BBN followed by Suzuki coupling with bromopolystyrene provided a precursor of polymer-bound benzaldehyde (4 Scheme 18). Hydrolysis gave the desired polymer-bound benzaldehyde (5 Scheme 18).
The utility of the polymer-bound benzaldehyde (5 Scheme 18) was demonstrated by the preparation of xcex1-branched benzyl alcohol as shown in Scheme 18. Addition of methylmagnesium bromide to the polymer-bound benzaldehyde (5 Scheme 18) provided polymer-bound secondary alcohol (6 Scheme 18), which was cleaved with bromine to yield xcex1-methyl-4-bromobenzyl bromide (7 Scheme 18). By choosing appropriate Grignard reagents, variety of secondary alcohols can be prepared. Such secondary alcohols can be further converted to other reactive species (for example bromide or tosylate) for solid-phase organic synthesis. 
Alternative method for producing polymer-bound xcex1-branched secondary alcohol (6 Scheme 18), in particular for a large-scale synthesis, is shown in Scheme 19. Starting from 4-bromoacetophenone and by following the similar reactions as described in Scheme 18, 2-(4-allyldimethylsilylphenyl)-2-methyl-1,3-dioxolane (3 Scheme 19) was obtained. Deprotection of dioxolane protecting group and subsequent reduction of the resulting 4-allyldimethylsilylacetophenone afforded a secondary alcohol (4 Scheme 19). Hydroboration of the secondary alcohol (4 Scheme 19) with 9-BBN followed by in situ Suzuki coupling with bromopolystyrene provided the previously described polymer-bound xcex1-branched secondary alcohol (6 Scheme 18). Conversion of the secondary alcohol to a bromine gave a polymer-bound xcex1-methyl benzyl bromide (6 Scheme 18).
Recently, a series of sulfonamide-containing 1,5-diarylpyrazole derivatives have been reported to block the activity of cyclooxygenase (COX-2). Since COX-2 is expressed during inflammatory conditions, inhibitors of this enzyme can be used for the treatment of variety of ailments, including rheumatoid arthritis and osteoarthritis.
The polymer-bound xcex1-branched secondary alcohol (6 Scheme 18) can be used to synthesize known COX-2 inhibitors on a solid support. For example, the polymer-bound xcex1-branched secondary alcohol (6 Scheme 18) can be oxidized to acetophenone derivative which can undergo a Claisen condensation reaction with various esters to form 1,3-dicarbonyl adducts. Reaction with (4-sulfamoylphenyl)hydrazine and subsequent cleavage produces the same 1,5-diarylpyrazole COX-2 inhibitor derivatives on a polymer support. 
As shown in Scheme 20, 1-allyldimethylsilyl-4-bromobenzene (1 Scheme 1) was used as a starting material for the preparation of phenylacetic acid bound to the polystyrene via the silyl linkage (1 Scheme 20). Sequential treatment of 1-allyldimethylsilyl-4-bromobenzene with t-butyllithium in THF followed by addition of ethylene oxide solution in THF to the reaction mixture afforded two carbon homologated alcohol (1 Scheme 8). The primary alcohol was oxidized in a solution of Jones reagent (CrO3, H2SO4) in acetone to give the carboxylic acid (2 Scheme 8). Hydroboration followed by Suzuki coupling of the carboxylic acid (2 Scheme 8) with bromopolystyrene gave the resin-bound carboxylic acid (1 Scheme 20).
Polymer-bound benzoic acid can be prepared by forming a Grignard reagent from bromophenyl derivative (1 Scheme 1) and reacting with CO2 followed by acid work-up to give 4-allyldimethylsilylbenzoic acid (2 Scheme 20). Esterification in methanol by catalytic amount of thionyl chloride gave methyl 4-allyldimethylsilylbenzoate (3 Scheme 20). This compound can be connected to the polystyrene resin by hydroboration followed by Suzuki coupling. 
4-Allyldimethylsilylphenethyl alcohol (1 Scheme 8) was attached to the bromopolystyrene under the standard coupling conditions (hydroboration with 9-BBN followed by a Suzuki coupling reaction) as shown in Scheme 21.
The resulting polymer-bound primary alcohol (1 Scheme 21) was converted to the bromide (2 Scheme 21). To demonstrate the utility of the resin-bound bromide (2 Scheme 21) in solid-phase organic synthesis, it was reacted with propylamine to obtain the polymer-bound secondary amine (3 Scheme 21), which can be cleaved with bromine to afford N-4-bromophenethyl-N-propylamine (4 Scheme 21). 
By following the similar reaction sequence as shown in Scheme 16, polymer-bound phenethylamine was synthesized. Mitsunobu reaction of 4-allyldimethylsilylphenethyl alcohol (1 Scheme 8) with N-Boc protected ethyl oxamate followed by hydrolysis afforded Boc-protected silylated phenethylamine (2 Scheme 22). Usual coupling conditions (Hydroboration with 9-BBN followed by Suzuki coupling) with bromopolystyrene as described in Scheme 16 can link the Boc-protected silylated phenethylamine (2 Scheme 22) to the polymer and can also be used for the reactions demonstrated in Scheme 16.
Using 3-carbon homologation reactions, 3-(4-allyldimethylsilylphenyl)-1-propanol (4 Scheme 22) was prepared as follows. Treatment of (1 Scheme 1) with t-butyllithium followed by reaction with 2-(3-bromopropoxy)tetrahydro-2H-pyran afforded THP protected silyl intermediate (3 Scheme 22). The THP group was removed to give the desired 3-(4-allyldimethylsilylphenyl)-1-propanol (4 Scheme 22). The 3-carbon homologated compounds, can also undergo the same reactions demonstrated in Scheme 16. 
Polymer-bound carboxylic acid compound (1 Scheme 20) is useful for solid-phase organic synthesis of amides and esters. This polymer-bound compound can be used for immobilizing molecules that can form a covalent bond with carboxylic acid function. By derivatizing the carboxylic acid with an appropriate chiral auxiliary, enantioselective substitution at the xcex1-position with various electrophiles can be achieved. This approach can provide a library of xcex1-substituted phenylacetic acids on the solid support which can be further utilized, e.g., reactions suggested in Scheme 20.
Scheme 23 illustrates a process for preparing the polymer-bound chiral auxiliary (1 Scheme 23). Hydroboration of chiral imidate (3 Scheme 8) with 9-BBN followed by Suzuki coupling with bromopolystyrene gave polymer-bound chiral imidate (1 Scheme 23). Cleavage of the resin (1 Scheme 23) with Br2 afforded bromo-substituted imidate (2 Scheme 23). Generation of potassium enolate from (1 Scheme 23) and subsequent treatment of the enolate with various alkyl iodide provides a library of polymer-bound xcex1-alkyl imidate (3 Scheme 23). Treatment of potassium enolate from (1 Scheme 23) with trisylazide affords a polymer-bound xcex1-azido compound (4 Scheme 23). 
Functionalized organozinc compounds can be generated under mild conditions using activated zinc developed by Rieke and many organozincs are commercially available. As shown in Scheme 24, palladium mediated cross-coupling reaction of silylated-iodobenzene (1 Scheme 24) to 3-ethoxy-3-oxopropylzinc bromide provided a 3-carbon homologated silyl compound (2 Scheme 24). This compound can be attached to the bromopolystyrene resin under the usual coupling conditions (hydroboration with 9-BBN followed by Suzuki coupling). The ester function can be further derivatized to various other functional groups, such as alcohol, aldehyde, and acid. In the same manner as described above, cross-coupling of silylated iodobenzene (1 Scheme 24) to (4-carbethoxyphenyl)zinc iodide gave silylated biphenyl system with ester function (3 Scheme 24). Thus, the cross-coupling reactions of silylated iodobenzene (1 Scheme 24) to other organozincs can be used to produce a variety of compounds. 
In Scheme 25, various functional group transformation reactions are shown. It should be noted that most of the silylated compounds with different functional groups synthesized either in solution phase or on the solid support are derived from the common intermediate (1 Scheme 1); however, it should be appreciated that the functional group transformation reactions shown in Scheme 24 can be applied to other aromatic systems, such as naphthalenes and heteroaromatics. 
Scheme 26 illustrates compounds and methods of the present invention which have aromatic systems other than phenyl group. As illustrated in Scheme 26, lithium-halogen exchange of 1,4-dibromonaphthalene followed by treatment with allylchlorodimethylsilane afforded silylated intermediate (1 Scheme 26). Grignard reagent of the intermediate (1 Scheme 26) was reacted with paraformaldehyde to afford silylated naphthalene methanol (2 Scheme 26). Alternatively, quenching of the lithiated intermediate (1 Scheme 26) with anhydrous DMF gave an aldehyde (5 Scheme 6) and subsequent reduction of this aldehyde with NaBH4 gave the silylated naphthalene methanol (2 Scheme 26). Hydroboration of (2 Scheme 26) and subsequent Suzuki coupling of the resulting borane complex produced polymer-bound hydroxy compound (3 Scheme 26). The polymer-bound hydroxy compound (3 Scheme 26) was brominated to give a polymer-bound bromide compound (4 Scheme 26), which can be used as a building block for various reactions, e.g. as demonstrated in Scheme 17.
Treatment of the polymer-bound bromide compound (4 Scheme 26) with excess Gly-OEt.HCl, DIPEA in DMF overnight followed by reaction of the resin with p-toluenesulfonyl chloride (TEA, DMAP in CH2Cl2) and cleavage with 50% TFA in CH2Cl2 afforded a naphthalene methyl-containing sulfonamide (5 Scheme 26). 
Scheme 27 shows applicability of the present invention to compounds containing heteroaromatic ring moieties. Selective lithiation of 2,5-dibromopyridine at C-5 position by n-butyllithium followed by quenching with anhydrous DMF gave 2-bromo-5-pyridinecarboxaldehyde (1 Scheme 27). Refluxing the aldehyde with ethylene glycol in the presence of p-toluenesulfonic acid provided 1,3-dioxolane analog (2 Scheme 27). Lithiation of (2 Scheme 27) with n-butyllithium followed by treatment with allychlorodimethylsilane afforded 2-(5-allyldimethylsilyl-2-pyridyl)-1,3-dioxolane (3 Scheme 27).
Reduction of 2-bromo-5-pyridinecarboxaldehyde (1 Scheme 27) with sodium borohydride gave a hydroxymethylpyridine (4 Scheme 27). Protection of this alcohol followed by silylation reaction gave 2-[(2-allyldimethylsilylpyridin-5-yl)methoxy]tetrahydro-2H-pyran (6 Scheme 27).
Alternatively, selective lithiation of 2,5-dibromopyridine at C-5 and treating with allychlorodimethylsilane gave 5-allyldimethylsilyl-2-bromopyridine (7 Scheme 27). The second lithiation of (7 Scheme 27) with n-butyllithium followed by treatment with anhydrous DMF yielded 5-allyldimethylsilyl-2-pyridinecarboxaldehyde (8 Scheme 27) which was reduced to the corresponding alcohol (9 Scheme 27). Compounds (3 Scheme 27), (6 Scheme 27), and (9 Scheme 27) can be attached to a polymeric resin and used in solid-phase synthesis of pyridine containing molecules. 
Application of the silylated building block strategy for polymer-bound aromatics were applied for thiophene as shown in Scheme 28. Lithiation of thiophene with n-butyllithium followed by treatment of with allylchlorodimethylsilane afforded 2-allyldimethylsilylthiophene (1 scheme 28). Lithiation of this compound with n-butyllithium followed by quenching with anhydrous DMF resulted in 2-allyldimethylsilylthiophene-5-carboxaldehyde (1 Scheme 6). Reduction of the aldehyde (1 Scheme 6) to alcohol (4 Scheme 28) with sodium borohydride and subsequent coupling with bromopolystyrene under usual conditions provided polymer-bound thienyl methanol compound (3 Scheme 28) which can be further derivatized to reactive halide (4 Scheme 28). These building block can be utilized for various reactions, including those shown in Scheme 17. 
Other polymeric linkers that can be use for Suzuki coupling reactions of various silylated organoborane complexes can be prepared as follows. Aminomethylated polystyrene resin (100-200 mesh) was reacted with 4-iodobenzoic acid (or 3-iodobenzoic acid) under usual peptide coupling conditions gave polymer-bound iodobenzoyl compounds (1 Scheme 29 and 2 Scheme 29).
Hydroboration of 4-allyldimethylsilylphenethyl alcohol (1 Scheme 8) followed by Suzuki coupling reaction with the linker (2 Scheme 29) resulted in polymer-bound phenethyl alcohol compound (3 Scheme 29) which can be cleaved with bromine to give 4-bromophenethyl alcohol (4 Scheme 29).
Amide bond formation of iodobenzoic acids with amino functionalized resins, such as Tentagel resin and PEGA, provides various other linkers which can be utilized for Suzuki coupling reaction for attachment of various compounds of the present invention.